Conventionally, in the printing plate-making field, solution waste generated along with the wet process for image forming materials has caused problems. In recent years, in terms of environmental protection and space saving, a decrease in processing solution waste has been strongly demanded. Accordingly, a technique for a photo-thermal photographic material has been desired for application to photographic techniques in which effective exposure is possible employing a laser image setter, and a clear and sharp black image with high resolution can be formed. As such techniques, several methods are well known, which are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,487,075, as well as in D. Morgan, "Dry Silver Photographic Materials", (Handbook of Imaging Materials, Marcel Dekker, Inc.) page 48, 1991, and the like. Because these photographic materials are commonly developed at a temperature of at least 80.degree. C., they are called thermally developable materials.
The thermally developable material forms images employing a thermal development and comprises photosensitive silver halide, a non-photosensitive reducible silver source (an organic silver salt), a reducing agent for the silver source and a silver toning agent if necessary, usually in a form of dispersion in an (organic) binder matrix. When a developable material for printing plate-making is employed for color printing, a plurality of film sheets, which are subjected to color separation for each color, are usually employed. These are printed onto each of the machine plates; the resulting plates are superimposed, and employed for printing. When film sheets which are subjected to a plurality of color separation are not precisely superimposed, a phenomenon called doubling occurs. Therefore, with developable materials for printing plate-making, it is important that the sizes are always identical after development, that is, repetitive accuracy is required.
However, when the thermally developable material described above is developed at a temperature of not less than 80.degree. C., conventionally, the above-mentioned repetitive size accuracy has not been sufficient, and when employed in color printing, they are not commercially viable. To overcome this problem, is described in Japanese Patent Publication Open to Public Inspection No. 10-10671 a technique in which resins such as polycarbonates, polyimides, etc., which tend not to be thermally contracted, are employed to prepare a support, instead of using conventionally employed polyethyleneterephthalates. This invention has been proven to assure the repetitive size accuracy. However, it has been found that when polyimide resin is used, as it is, to prepare a support, the developable material itself results in a brown tint, which is not commercially viable.